Most laboratories do not measure LDL cholesterol directly — they calculate it from total cholesterol, HDL cholesterol and triglycerides. This calculator uses the Sampson/NIH Equation 2, published in 2020 and validated for triglycerides up to 800 mg/dL, and shows the older Friedewald estimate and non-HDL cholesterol alongside it.
- What it estimates
- LDL cholesterol from a standard lipid panel
- Equation
- Sampson / NIH Equation 2 (2020)
- Inputs
- Total cholesterol, HDL cholesterol, triglycerides
- Validated range
- Triglycerides up to 800 mg/dL (9.0 mmol/L)
- Categories
- NCEP ATP III LDL classification
Formula
Sampson / NIH Equation 2 (Sampson et al., JAMA Cardiology 2020)LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG × NonHDL/2140 − TG²/16100) − 9.44
- TC
- — Total cholesterol, mg/dL (mmol/L × 38.67)
- HDL
- — HDL cholesterol, mg/dL (mmol/L × 38.67)
- TG
- — Triglycerides, mg/dL (mmol/L × 88.57)
- NonHDL
- — TC − HDL, mg/dL
Friedewald (LDL = TC − HDL − TG/5) assumes VLDL cholesterol is always one fifth of triglycerides, which becomes inaccurate as triglycerides rise and is not valid at 400 mg/dL or more. The Sampson equation was developed against the ultracentrifugation reference method and calculates LDL at triglycerides up to 800 mg/dL with about the accuracy Friedewald achieves below 400. Martin-Hopkins is another validated method, but it relies on a 180-cell table of factors and is not implemented here.
LDL Cholesterol Calculator examples
| Input | Result | Category |
|---|---|---|
| TC 200, HDL 50, TG 150 mg/dL | 123 mg/dL | Near optimal/above optimal |
| TC 170, HDL 60, TG 90 mg/dL | 93 mg/dL | Optimal |
| TC 240, HDL 45, TG 200 mg/dL | 158 mg/dL | Borderline high |
| TC 140, HDL 45, TG 250 mg/dL | 55 mg/dL | Optimal |
| TC 260, HDL 38, TG 500 mg/dL | 131 mg/dL | Borderline high |
| TC 300, HDL 55, TG 120 mg/dL | 224 mg/dL | Very high |
| TC 280, HDL 30, TG 950 mg/dL | — mg/dL | Direct LDL needed |
How is LDL cholesterol calculated?
A standard lipid panel measures total cholesterol, HDL cholesterol and triglycerides. LDL is then estimated by subtracting HDL and an estimate of VLDL cholesterol from the total. The equations differ in how they estimate VLDL cholesterol from triglycerides.
| Method | Year | VLDL estimate | Valid range |
|---|---|---|---|
| Friedewald | 1972 | Fixed: TG ÷ 5 | TG below 400 mg/dL |
| Martin-Hopkins | 2013 | TG ÷ a factor from a 180-cell table | Derived from 1.35 million US lipid profiles; not implemented here |
| Sampson / NIH Equation 2 | 2020 | Equation using TG and non-HDL | TG up to 800 mg/dL |
At ordinary triglyceride levels the equations usually agree within a few mg/dL. They diverge most when triglycerides are high or LDL is low, which is exactly where treatment decisions are often being made.
Why use the Sampson equation instead of Friedewald?
Friedewald's fixed ratio of triglycerides to VLDL cholesterol holds reasonably well in people with normal lipids, but triglyceride-rich particles carry proportionally less cholesterol as triglycerides rise. Friedewald then tends to underestimate LDL, and it is not considered valid at triglycerides of 400 mg/dL or more.
Sampson and colleagues at the NIH derived their equation against beta-quantification, the ultracentrifugation reference method, in a large clinical laboratory population. It estimates LDL at triglycerides up to 800 mg/dL about as accurately as Friedewald does below 400, which lets laboratories report a calculated LDL for many patients who would otherwise need a direct measurement.
What do the LDL cholesterol ranges mean?
The NCEP Adult Treatment Panel III (2001) classification is still the most widely quoted way of describing an LDL result on its own:
| Category | mg/dL | mmol/L (approx.) |
|---|---|---|
| Optimal | Below 100 | Below 2.59 |
| Near optimal/above optimal | 100–129 | 2.59–3.35 |
| Borderline high | 130–159 | 3.36–4.13 |
| High | 160–189 | 4.14–4.90 |
| Very high | 190 and above | 4.91 and above |
These labels describe the number, not the person's risk. Whether a given LDL needs treatment depends on age, existing cardiovascular disease, diabetes, blood pressure, smoking and other factors.
How do current guidelines use LDL cholesterol?
The 2018 AHA/ACC multisociety cholesterol guideline frames LDL thresholds in the context of overall cardiovascular risk rather than as stand-alone targets. A few groups are identified directly by LDL level:
- Severe primary hypercholesterolaemia (LDL 190 mg/dL or higher): high-intensity statin therapy is recommended without calculating 10-year cardiovascular risk.
- Adults aged 40 to 75 with diabetes and LDL of 70 mg/dL or higher: moderate-intensity statin therapy is recommended without calculating 10-year risk.
- Other adults aged 40 to 75 in primary prevention: a clinician–patient risk discussion, informed by estimated 10-year risk, comes before any decision to start a statin.
People with established cardiovascular disease are managed under separate, more intensive recommendations. Other guideline bodies, including European societies, use different thresholds and targets.
What is non-HDL cholesterol, and why does it matter?
Non-HDL cholesterol is simply total cholesterol minus HDL cholesterol. It counts the cholesterol in every potentially atherogenic particle — LDL, VLDL and their remnants — rather than LDL alone.
Because it needs no estimate of VLDL, non-HDL cholesterol stays valid at any triglyceride level. When triglycerides are too high for any LDL equation, it is still reported here, and it is a useful second number whenever triglycerides are raised.
When is calculated LDL unreliable?
- Triglycerides above 800 mg/dL (9.0 mmol/L): no equation here is valid, and a direct LDL measurement is needed.
- Triglycerides of 400 mg/dL or more: Friedewald is not valid; this calculator reports it as such.
- Inconsistent inputs — for example HDL equal to or higher than total cholesterol, which is not possible. The calculator flags this instead of returning a number.
Frequently asked questions
Why does my calculated LDL differ from my lab report?
Laboratories use different equations — Friedewald, Martin-Hopkins or Sampson — and some measure LDL directly. At normal triglyceride levels the difference is usually a few mg/dL. It grows when triglycerides are high or LDL is low. Check your report to see which method the laboratory used.
What is the Sampson or NIH equation?
It is an LDL cholesterol equation published in 2020 by Sampson and colleagues at the US National Institutes of Health. It estimates VLDL cholesterol from both triglycerides and non-HDL cholesterol, and was validated for triglycerides up to 800 mg/dL, twice the limit of the older Friedewald equation.
Why is Friedewald not valid above 400 mg/dL triglycerides?
Friedewald assumes VLDL cholesterol is always one fifth of triglycerides. As triglycerides rise, that ratio changes and the equation increasingly underestimates LDL. It is not considered valid at triglycerides of 400 mg/dL or more, so this calculator reports it as not valid in that range rather than giving a number.
What LDL level is considered too high?
Under the NCEP ATP III scheme, 130 to 159 mg/dL is borderline high, 160 to 189 high and 190 or above very high. Current US guidelines judge the need for treatment by overall cardiovascular risk, but an LDL of 190 mg/dL or more warrants high-intensity statin consideration on its own.
Can I enter cholesterol in mmol/L?
Yes. Switch the unit toggle to metric. Cholesterol values are converted with 1 mmol/L = 38.67 mg/dL and triglycerides with 1 mmol/L = 88.57 mg/dL, because the equations are defined in mg/dL. Results are shown back in mmol/L.
What should I do if my triglycerides are above 800 mg/dL?
Ask for a direct LDL cholesterol measurement, because no calculation is reliable at that level. Non-HDL cholesterol is still valid and is shown here. Triglycerides that high also need medical attention in their own right, so discuss them with your clinician.
Sources
- A New Equation for Calculation of Low-Density Lipoprotein Cholesterol in Patients With Normolipidemia and/or Hypertriglyceridemia — Sampson M et al., JAMA Cardiology (PubMed), 2020
- Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge — Friedewald WT, Levy RI, Fredrickson DS. Clinical Chemistry (PubMed), 1972
- Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels from the standard lipid profile — Martin SS et al., JAMA (PubMed), 2013
- Executive Summary of the Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) — JAMA (PubMed), 2001
- 2018 AHA/ACC multisociety Guideline on the Management of Blood Cholesterol — Grundy SM et al., Circulation (PubMed Central), 2018